This subnet mask cheat sheet is one table: every subnet mask from /8 to /32, in decimal and binary, next to its wildcard mask, block size, and usable host count. Print it in A4 or US Letter and keep it by your keyboard for the CCNA exam or for the job.
Is it a free download? Yes. Drop your email below and it lands in your inbox. No payment.
What This Subnet Mask Cheat Sheet Covers
A subnet mask cheat sheet only works if you can find the row you need in about two seconds. This one’s built for that: one CIDR table, /8 through /32, decimal and binary side by side, so you’re not translating 255.255.255.192 into 11111111.11111111.11111111.11000000 in your head during a timed exam.
Here’s the mistake that costs people more marks than the math itself. A /26 gives you 64 addresses total, not 62. The network address and the broadcast address are still addresses, they’re just not usable ones. Miss that distinction and you’ll misread a question that asks for “addresses” instead of “usable hosts.” That’s why this sheet keeps total addresses and usable hosts as two separate columns instead of one, so the gap is visible instead of memorized.
Knowing the table is half the job. The other half is applying it on a live network, and that’s where the CCNA Lab Workbook comes in: 75 labs in EVE-NG and Packet Tracer, with IPv4 and IPv6 addressing and subnetting built into real topologies.
Subnet Mask vs Wildcard Mask: The 255-Minus Shortcut
A wildcard mask is a subnet mask with every bit flipped. Cisco uses it in ACLs and OSPF network statements instead of the subnet mask you’d use everywhere else, and the fastest way to convert between them is to subtract each octet from 255. For a /24, the subnet mask is 255.255.255.0, so the wildcard mask is 0.0.0.255. For a /26, 255.255.255.192 becomes 0.0.0.63. This sheet lists both side by side for every prefix, so you’re not doing that subtraction mid-exam.
What’s Inside the Subnet Mask Cheat Sheet
- Full CIDR table, /8 to /32: subnet mask, wildcard mask, block size, total addresses, and usable hosts for every prefix, decimal and binary
- Binary column: the actual 1s and 0s behind each mask, next to the decimal shortcut, so you can check your work either way
- Powers-of-2 reference: host bits mapped straight to usable hosts, in both directions, no calculator needed
- IPv4 classes and private ranges: Class A through E, plus the three private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) and the loopback block. Our Private IP Address Ranges and IP Classes Explained guide walks through why those three ranges exist and where each one actually shows up on a real network.
- IPv6 prefix quick-reference: the /48, /56, and /64 prefixes you’ll actually run into on the exam and on the job
- Subnetting shortcuts, one page: the magic-number method, the wildcard-mask shortcut, the broadcast-address formula, and the /30-for-point-to-point rule
- Printable, A4 and US Letter: built to print single-sided and sit next to your keyboard, not just live in a browser tab
New to IPv6 addresses? Read what IPv6 is first.
Go deeper
This table gets the lookup instant.
The CCNA Lab Workbook is 75 hands-on labs across 950 pages in EVE-NG and Packet Tracer, so every subnet in this sheet gets built on a real topology instead of staying on paper.
See the CCNA Workbook →Subnet Mask Cheat Sheet or Subnet Calculator: When Each One Wins
A subnet calculator and a subnet mask cheat sheet solve two different problems. A calculator is built for a one-off: plug in an address and a prefix, get the answer, move on. A cheat sheet is built for repetition, the fortieth time this week you need to know what a /27 looks like, where opening a calculator tab each time is slower than glancing at a printed page.
For memorizing the table ahead of the CCNA exam, the cheat sheet wins outright, since you can’t open a calculator during the real thing. For subnetting an actual production network, run the calculation properly instead of trusting memory. A cheat sheet catches “what’s the mask for /27 again,” not a real IP plan.
Who It’s For
- CCNA 200-301 candidates who want the subnetting math automatic before exam day, not worked out from scratch each time
- Junior network engineers who want a ten-second lookup instead of opening a subnet calculator for every VLAN
- Readers of our Subnetting Explained guide who want the tables from that article on paper
- Anyone doing VLSM practice who needs block size and host count in the same place
- Anyone who mixes up VLANs and subnets, a genuinely common confusion: our VLAN vs Subnet: What’s the Difference? guide draws the line between the two before you dive into this table
It’s a lookup table, not a lesson. If you haven’t seen why the block-size method works yet, start with Subnetting Explained. This sheet is what you keep open once you already get it. Ready to use it on real routers? The 75 hands-on labs in our CCNA workbook are the next step.
Printable Format: A4 and US Letter
Two sizes in the same download: A4 for everywhere outside North America, US Letter for inside it. Both are one page per side, so it prints clean on a single sheet, front and back, no scaling issues at the printer.
